Anna Gorbenko1 Nafisa Noor1 Sadid Muneer1 Raihan Sayeed Khan1 Faruk Dirisaglik2 Adam Cywar3 Yu Zhu4 Ali Gokirmak1 Helena Silva1


1, University of Connecticut, Storrs, Connecticut, United States
2, Eskisehir Osmangazi University, Eskisehir, , Turkey
3, Analog Devices, Norwood, Massachusetts, United States
4, IBM T.J. Watson Research Center, Yorktown Heights, New York, United States

Resistance drift of the amorphous and on-oxide phase change memory (PCM) devices raises a significant concern in the long term reliability of these cells when they are used in computer memory [1]. The resistance of amorphous Ge2Sb2Te5 (GST) cells and other amorphous phase change memory devices slowly increases over time until a certain point at which it starts decreasing due to crystallization[2]. Resistance drift depends on temperature, original programmed resistance, the waveform used to reset the devices, and the shape and dimensions of the cells[2]-[3].
In this work we compare the resistance drift behavior of suspended and on-oxide GST line cells. The suspended cells are coated by a 15 nm layer of silicon nitride after being suspended in air, while the on-oxide cells rest on silicon dioxide and only the sides and the top surface are capped by 15 nm of silicon nitride. The results, obtained over several months, show that the suspended GST wires have a noticeably larger resistance drift coefficient as compared to the on-oxide wires, and also exhibit significantly more variable resistance behavior. The increase in drift coefficient and variability may be associated with differences in the mechanical stress of the suspended wires compared to the on-oxide ones as well as the different interfacial properties of these devices. Experimental results from a large number of devices of varying dimensions will be presented and discussed.

[1] M. Rizzi, et al. “Role of mechanical stress in the resistance drift of Ge2Sb2Te5 films and phase change memories.” American Institute of Physics, 2011.
[2] N. Noor, et al. “Phase-Change Materials and Their Applications—Memories, Photonics, Displays and Non-von Neumann Computing.” 2017 MRS Spring Meeting and Exhibit, MRS, 2017.
[3] N. Noor, et al. “An experimental study on waveform engineering for Ge2Sb2Te5 phase
change memory cells.” 2015 MRS Fall Meeting and Exhibit, MRS, 2015.